Electric switch.



C. T. HENDERSON 6; W. C. STEVENS.

ELECTRIC SWITCH.

APPLICATION FILED SEPT. 14. 1914.

1 69,554. Patented June 11, 1918.

UNITED sTATEs' PATENT OFFICE.

GLA'RIIT. :HENDERSON, OF MILWAUKEE, WISCONSIN, AND WILLIAM C. STEVENS, OF NEW YORK, 11 Y., ASSIGNORS'TO THE CUTLER-HAM1VLER MFG. 00., OF MILWAUKEE, WISCONSIN, A CORPORATION OF WISCONSIN.

ELECTRIC SWITCH.

Specification of Letters latent.

Patented June 11, 1918.

Application filed September 14,1914. Serial No. 861,601. r

To all whom it may concern:

Be it known that we, CLARK T. HENDER- SON and VILLIAM C. Srnvnxs, citizens of the United States, residing, respectively, at Milwaukee, inthe'county of Milwaukee and State of lVisconsin, and New York city, in the State of New York, have invented new and useful Improvements in Electric Switches, of which the following is a full, clear, concise, and exact description, reference being-had to the accompanying drawing, forming a part of this specification.

This invention relates to improvements in electric switches.

Switches have been devised called series switches in which a single coil operates the contacts and the magnetic circuit is so formed that the coil will not close the contacts so long as the current to which it is subjected is above a pre-determined value. This magnetic circuit has a portion of restricted cross-section which becomes saturated when the current in the coil is above a certain limit. A shunt magnetic circuit is provided around the restricted circuit. lVhen the coil is energized with a high current,"the excess flux passes through the shunt circuit and acts on a means which prevents the switch fromoperating. When current in the coil decreases, the flux dies out of the shunt circuit, the holding means becomes inactive and the switch is allowed to operate. The restricted magnetic circuit which is a necessary element in these switches gives rise to several limitations hereinafter pointed out.

Switches-of the above mentioned type are often equipped with contacts which are closed against the pressure of a spring. It is desirable that the movement against the spring pressure be for a considerable distance in order to compensate for wear on the contacts. The force necessary to close the contacts against the spring pressure is larger-than that necessary to start the movement thereof. For this'and other reasons it follows that the force acting on the contacts should be at a maximum value as the contacts are moved to and held in closed posi tion.

Therestriction on the magnetic circuit in switches otthe type described limits the maximum closing pull for any given size of switch. When the o crating coil and the movable parts are ma e of proper size for a given current, the restricted portionlof the magnetic circuit must be limited to a-proper capacity to insure that the switch will oper ate when the current decreases to a predetermined value. The capacity of the circuit when so :limited is such that it .is substantially saturated by the actuating flux passing through it at the time the switch starts to operate. It, therefore, cannot accommodate an increase in lines of force and does not act as a return path'for the increase in flux. The result is, @that as the armature moves to decrease its air gap, theadditional flux which would normally tend t0-llll6&,(l through the armature and exert an additional pull thereon does not do so forthe reason that the saturated restricted magnetic circuit does not provide a returnpath from thearmature. Since there is no substantial increase in the amount of flux passing through the armature as it decreases its air gap, the pulldoes notincrease to :the high maximum desirable during final closing movement. Curve A in Fig. 3 illustrates the change in pull on the armature as the air gap is dccreasedin a structure in which the magnetic circuit is restricted in capacity. It will be noted that .the';pull does not :increase rapidly when the air gap is small. Curve B shows the increase in pull on the armature in the same sized structure. having a means providing a magnetic circuitof large capacity.

It will thus be seen that the maximum pull'obtaina'ble in a given size of switch is limited by the capacity of the restricted magnetic circuit. An increase inpull onia given size of contacts obtained by increasing the size of the coil, the movable member and'the magnetic circuit, or either of them, above what would otherwise be necessary to secure operation on predetermined current is not desirable for the reason that the switch is more expensive and an increased space for installation is necessary.

One of the objects of the present inventian is to provide a magnet of the solenoid and plunger type with a means for increasing the pull on the plunger after it has responded.

Another object of the invention is to provide anelectromagnetic structure in which an armature of the plunger type is actuated to and held in closed position in a positive, forceful manner.

Another object of the invention is to provide a switch of the solenoid and plunger type in which the contacts will be firmly forced to and held in closed position regardless of limitations in the amount of flux available to start the switch.

Another object of the invention is to provide a means for completing an additional magnetic circuit for the flux in a switch of the solenoid and plunger type having a restricted magnetic circuit to thereby in crease the pull on the armature as the switch closes.

Another object of the invention is to provide an electromagnetic structure of the solenoid and plunger type in which an additional path is provided for the flux after the movement of the plunger has been initiated.

Various other objects and advantages of my invention will hereinafter appear.

The accompanying drawing illustrates an embodiment of the invention and in said drawing:

Figure 1 is a side elevation of a switch embodying the invention.

Fig. 2 is a cross section view of the restricted magnetic circuit.

Fig. 3 is a pull curve diagram illustrating the operating characteristics of the switch.

The switch comprises an electromagnetic winding or coil 2, a plunger 3, a movable contact 4 carried by the plunger, and a pair of stationary contacts 5 cooperating with the movable contact and adapted to be engaged thereby. The coil, plunger and contacts may be of any suitable form.

A lower bracket 6 of magnetic material forms part of the magnetic circuit. This bracket supports the coil 2 and a brass tube 7 inside of the coil in the structure shown, but it is obvious that the tube 7 and the coil 2 might be supported in any other desirable manner. Above the coil is an upper bracket 8 of magnetic material to which is pivoted at 9 a magnetic arm 10 whose end 11 cooperates as an armature across the gap 12 with the outer end or pole piece 12' of lower bracket 6. The arm 10 has an inner end 13 of restricted cross section pivoted at 11 to a stem 15 which passes through an opening in bracket 8 and is attached to the plunger 3. The plunger 3, stem 15 and arm 10 are movable together and are normally biased by gravity to the open osition shown. A spring 16 may be adde to supplement the action of gravity if desired.

The flux resulting from the energization of coil 2 normally follows the main magnetic circuit from plunger 3 to stem 15, through the restricted inner end 13 to arm 10. thence across air gap 12 to pole piece 12 and across another air gap to plunger 3. A collar 17 of non-magnetic material surrounds the restricted end 13 of arm 10 and acts as a short circuited coil to dampen a sudden increase in flux through the restricted portion.

The stem 15 also carries a recessed disk 18 of magnetic material which is adjustably secured to the stem so that the air gap between the disk 18 and the bracket 8 may be adjusted when the arm 10 is in open position as shown. In order to prevent the recessed disk 18 from coming into actual contact with the bracket 8, a suitable stop is provided which, in this case, comprises brass nuts 19 which engage the bottom of an enlargement of the plunger 3. It is to be understood that the stop may be otherwise shaped and located. The stop insures that the small air gap is normally maintained between disk 18 and bracket 8 when the switch is in open position.

When the coil is energized by high current, the restricted section 13 of the arm 10 becomes saturated with flux and the lines of force set up by coil 2 must take another path. These lines follow a path through the disk 18 across the small air gap to bracket 8, through pivot 9 to arm 10 and across air gap 12 to pole piece 12 and core 3. The lines of force across the gap between the disk 18 and the bracket 8 exert a magnetic pull on the disk 18 which acts in opposition to that set up by the lines of force across the gap 12. As long as the current energizing the coil 2 is high, the pull on the disk 18 is effective to prevent operation of the switch.

As the current in the coil decreases, less flux asses through disk 18 to bracket 8 until a po1nt is reached where the restricted section 13 carries the greater proportion of the flux. When this point is reached, there is very little pull on the disk 18 and, therefore, very little opposition to movement of the arm 10 and the same is pulled to closed position by the flux across the gap 12.

Switches of this type generally operate under conditions where they are suddenly energized by a high current and it is desirable to have them automatically locked open until the current has died down to a safe limit. The locking out action due to the pull on the disk 18 by the flux passing to the bracket 8 is accentuated by means of the brass collar 17 which acts as a short circuited coil around the restricted section 13. This collar opposes a sudden increase in flux through section 13 with the result that when the switch is suddenly energized, the short circuited collar tends to choke off the flux through section 13 thereby forcing y it through the path including the disk 18 and bracket 8 and insuring that the switch will be locked open when the coil is suddenly energized.

Substantially all the actuating flux which passes across the gap 12 as the switch starts to close, must pass through the restricted section 1 3 of the magnetic circuit since a prerequisiteto operation is that a small pull and, therefore, a smallsamount oi flux-be present at the gap between disk .18 and bracket 8. The starting flux is consequently limited by the size of the-restrictedportion of the magnet-iccircuitnecessary to insure that the switch will operate when the current dies down to a safedimit.

The structure shown inthe accompanying drawing illustrates one former a means for avoiding the limitation resulting from the restricted magnetic circuit. The plunger 3 carries an enlargementQO in the formof a frustum of a cone. Projecting outwardly around the opening in the bracket 8 is a ring 21 whose inner surface is shaped to correspond to the angleofthe sides of the frustum 20. As the switch closes the frustum 20 moves up 'ardly with the plunger 3 and establishes a magnetic circuit from plunger 3, through frustumQO to collar21, bracket 8, arm 10, air gap l2 andpole-piece 12 to core 3. This circuit constitutes in effect a magnetic short circuit around the restricted section 13 which has previously acted as a throttle on the flux. The new circuit thus established is of ample capacity to provide a good return path for any increase in lines of force through the arm 10 and consequentlyas thearm 10 approaches the pole piece 12, an additional amount of flux passes through it and an increasedpull is exerted thereon. An added pull is also exerted on the movable structure by reason of the pull on frustum 20.

By ,the use of the conical shape for the part 20, the reluctance of the air gap between it and the ring-21 is decreased more rapidly than the reluctance of the air gap 12, thereby tending to smooth out the pull curve of the structure.

The additional magnetic circuit completed during closing movement of the switch removes the limitation on the closing pull heretoforeencountered in switches having a restricted magnetic circuit. The switch is closed smoothly and with an increasing force which reaches a maximum during final movement. The contacts are thereby wiped home and held in a positive and forceful manner against the spring pressure.

It should be understood that the word armature as usedherein is intended to be given a broad meaning to include many other structures.

It is to be understood that the structure shown is for the purposes of illustration only and that other structures may be devised which come within the spirit and scope of the appended claims. i i

Having described our invention, What We claim and desire to secure by Letters Patcut is:

1. An electromagnetic mechanism having amovable plunger, amagnetic circuit actingto move the-plungcnin one direction, a second magnetic circuit acting to hold the plunger against movement, and a third magnetic circuit adapted to be vclosed as the plunger ,moves for increasing the moving force a fter it has 'overcomethe holding'force.

A11 electromagnetic .mechanism having anarmature at least aportion of which constitutes a plunger, said armature being biased toonegposition andmovable to another positiommeansfor causing: the electromagnct to hold the armature inits first position when the initial current through the winding is high and to move .it tothesecoud position whenthe current decreases to a, predetermined value, .and a1magnetic circuit controlled by movement of the armature 'for causing the electromagnet to.exert, a force on said armature ;to assist the closing force after the movement of the armature has been initiated.

An electromagnetic mechanism having anarmature at least a portion of which constitutes a movable plunger, an operating winding forthe armature,means including a magnetic circuit of limited capacity for preventing movementoi. the armature when the winding is initially energized above a predetermined mine, and a magnetic circuit in shunt to the circuit of limited capacity and adapted to be controlled by movement ofthe armature forincreasingthe pull on the armature after movement.-thereof has been initiated.

An electromagneticmechanism having anarmature at least a portion of which con stitutes a movable plunger, an operating winding for the armature, means including a magnetic-circuit of limited capacity for preventing movement of the armature when the illltlal current in the winding is above a predetermined fvalue, and. said plunger i bemg adapted';to increase the capacityof-the magnetic circuit-after movementzof the armature has been initiated to thereby increase the actuat ng }pull on the armatureduring movement thereof.

5. An elect-r0111agnetic mechanism having an armatureat leasta portion of which constitutes ,a movable plunger, an operating winding for the armature, meansibv which said winding exerts a pull to move said armaturennd an opposing pull to prevent movement thereof when the initial current in the winding is above a predetermined value, and said plunger being adapted to cause the holding pull to assist the moving pullafter the moving-pull has overcome the holding pull.

6; An electromagnetic mechanism having an armature at least a portion of which constitutes a movable plunger, an operating winding for the armature, a magnetic circuit having a portion of limited capacity, a

magnetic circuit in shunt to said portion of limited capacity, said shunt circuit including said plunger, said plunger being arranged to open the shunt circuit'as it is moved, and said plunger being adapted to complete a second circuit in shunt to the limited capacity circuit during movement of the armature to thereby increase the pull on the armature during movement thereof.

7. An electromagnetic mechanism having an armature at least a portion of which constitutes a movable plunger, an operating winding for the armature, a magnetic circuit of limited capacity, means controlled by excess flux for preventing movement of the armature when the winding is initially energized above a predetermined value, and said plunger being adapted when actuated to cause the excess flux to assist in moving said armature after movement thereof has been initiated.

8. An electromagneticmechanism having an armature at least a portion of which constitutes a movable plunger, an operating winding for the armature, a magnetic circuit of limited capacity, means controlled by excess flux for preventing movement of the armature when the winding is initially energized above a predetermined value, and said plunger being adapted when actuated to cause some of the exces flux to be reversedin its direction of operation on the armature so that it assists in moving the armature after movement thereof has been initiated.

9. An electromagnetic mechanism having an armature at least'a portion of which constitutes a movable plunger, an operating winding for the armature, means for causing the winding to exert a magnetic pull in one direction to move the armature and a pull in another direction to restrain movement thereof, and said plunger being adapted to cause an additional actuating pull to be exerted after movement of the armature has been initiated. I

10. An electromagnetic mechanism having an armature at least a portion of which constitutes a movable plunger, an operating winding for the armature, means for causing the winding .to exert a magnetic pull'in one direction to move the armature and a pull in another direction to restrainmovement thereof, and saidplunger being adapted to cause some of the restraining flux to assist the actuating force after the actuating force has overcome the restraining force.

11. An electromagnetic switch having an armature at least a portion of which consti- Copies of this patent may be obtained for tutes a plunger, an operating winding for the armature, means including a magnetic circuit of limited capacity for preventing movement of the armature when the initial current in the winding is above a certain value and for moving said armature when the current decreases to a predetermined value, said plunger being adapted to complete a magnetic circuit in shunt to said circuit of limited capacity during closing movement of the switch to thereby increase the actuating pull on the armature as the switch closes.

1'2. An electromagnetic switch having a movable contact controlling plunger, an energizing winding, an armature connected to said plunger and adapted to operate the same, a magnetic circuit of limited capacity between said plunger and armature, a second magnetic circuit between said'plunger and armature forming a path for the excess flux from the first circuit, said second circuit including a second armature connected to the plunger and adapted to act in opposition to the first to prevent movement of the plunger when the winding is initially highly'energized, and a third armature connected to the plunger for completing a magnetic circuit in shunt to the limited capacity circuit after movement of the plunger has been initiated to thereby increase the actuating force on the plunger.

13. An electromagnetic switch having a movable contact controlling plunger, an armature connected to said plunger and adapted to operate the same, a magnetic circuit. of limited capacity between said plunger and armature, a second magnetic circuit between said plunger and said armature adapted to act in opposition to the first magnetic circuit to prevent movement of the plunger when the winding is energized above a predetermined value, and a third magnetic circuit adapted to be closed by movement of said plunger to produce a shunt path for the flux around said circuit of limited capacity.

In witness whereof, we have hereunto subscribed our names in the presence of two witnesses.

' CLARK r. HENDERSON. WILLIAM c. sTEvENs.

lVitnesses for Henderson:

L. A. WATSON, J. S. BROCK, Witnesses for Stevens:

' QH. DATE,

RALPH A. CovELL.

five cents each, by addressing the Commissioner of Patents,

Washington, I). G. c I 

